The present invention relates to the field of osteal prostheses. The object of the invention is to provide a new prosthesis and a method for producing the latter.
The general technique of implanting metal parts for replacing or consolidating bones or osteal articulations is already known. Of course, the shape of the implant must be adapted to the concerned bone part. This is for example the case of prostheses adapted for the articulations of the hip or knee.
Metal implants were first employed fixed in the living bone by a cement, in particular a cement based on acrylic resin. This fixing technique employing cement results in many drawbacks, among which may be mentioned a defective performance of the prosthesis owing to risk of the cement breaking up and intolerance on the part of the organism and the bone tissue of the foreign body formed by the cement.
This is why prostheses were proposed, the securing of which did not require the use of cement. For this purpose, the surface of the implant was rendered rough or porous so as to permit the development or growth of the bone tissue on the surface of the prosthesis itself and thereby ensure its anchoring in the bone. The drawbacks of the technique of securing with cement are practically completely eliminated by this technique, but the latter may be still further improved. By way of illustration, it may be estimated that the use of cement results, in the case of hip prostheses, in more than 25% of failures owing to the loosening of the implant in the bone. This percentage of failures is substantially reduced when a porous or rough surface is provided on the implant, but in at least 10% of the cases it is necessary for many various reasons to intervene surgically again in order to replace the prosthesis. But, in this case, the prosthesis cannot be simply extracted, since, owing to the extremely strong anchoring effect created by the development or growth of the bone tissue, a delicate surgical intervention is necessary with a cutting of the bone in order to remove and replace the prosthesis.
By way of the prior documents illustrating the prior art, there may be mentioned German Pat. No. 837,294, French Pat. No. 72,27,966 (publication No. 2,194,123), U.S. Pat. No. 3,905,047 and French patent application published under No. 2,356,465. The teaching of these various patents may be briefly summarized as follows.
German Pat. No. 837,294 relates to a prosthesis whose shaft (or stem) has an outer surface which is splined generally in a direction parallel to the mean axis. No precise information is given concerning the splines which may have any shape, number and size. Further, their profile may have an acute angle or be rounded. In fact, these splines cannot ensure a sufficient retaining effect on the part of the bone tissue and, moreover, the rectilinear longitudinal profile of these spline does not allow an extraction of the prosthesis stem under satisfactory conditions.
French Pat. No. 72,27,966 (publication No. 2,194,123) proposes a prosthesis adapted to be secured without cement and comprising a porous outer surface. Once placed in position, such a prosthesis cannot be extracted. Further, the conditions under which such a prosthesis is obtained result in a risk of corrosion of the surface. The latter is also rendered more fragile which, under the effects of the high stresses, may create weak zones and finally result in the fracture of the prosthesis.
U.S. Pat. No. 3,905,047 concerns a prosthesis having surface irregularities. Once placed in position, such a prosthesis cannot be extracted by a simple tractive force owing to the development of the bone tissue, which constitutes one of the features claimed by the patent.
French patent application published under No. 2,356,465 relates in particular to a prosthesis comprising on its outer surface a covering constituted by balls or spherules. The latter are distributed in a random manner so as to ensure a solid anchoring effect. Such a prosthesis cannot be extracted in the case of an accident without a special surgical intervention.
Therefore, at the present time there are clearly no osteal prostheses to the knowledge of the applicant which may be secured in position without cement, which are capable of being effectively retained in the bone tissue after development of the latter and yet which may be extracted, if required, without the obligation to effect a delicate surgical intervention.